AlgalonObserver is the Algalon raid assistant of HordeYakka (Jubei'Thos). It was written before Deadly Boss Mods got all its warnings, and by now there is a certain amount of overlap between the two. It does however provide a few features not currently available in DBM:

Collapsing Star health tracking. A dedicated window with health bars for known Collapsing Stars provide at-a-glance overview to help healers and the star-destroyer plan things. Simply "mousing" over a Collapsing Star makes it known to everyone running AlgalonObserver in the raid, as will targeting one.
Low-health warning for Collapsing Stars. Annoying beeping when a star is about to blow gives the healers a heads-up about incoming raid damage.
Big countdown of both Big Bang and Cosmic Smashes in the center of the screen, enabling accurate timing to jump through a black hole and/or pop cooldowns.

AlgalonObserver activates automatically when you enter the Celestial Planetarium, and deactivates when you leave it. It was meant to deactivate as soon as you defeat Algalon, but I haven't had a chance to work out why I didn't get that to work. Since it's only a minor nuisance, I might not get around to fixing that.

Configuration is available via "/algalon config", or the regular "ESC->Interface->AddOns->AlgalonObserver" interface. For more command line options, just type "/algalon" (without the quotes).

With HordeYakka having achieved its goal of getting Algalon down (though beaten by Asgard and Kokoda - well done guys), we're now releasing this add-on to help others. Continued development is likely to be minimal, as we'll now be focusing on Trial of the Grand Crusader instead.